1. Field of the Invention
The present invention relates to an exposure control device for use in a camera, and more particularly to an exposure control device adapted for photographing an object illuminated by flash light.
2. Description of the Prior Art
In general, photographing with a camera takes place in a natural light exposure mode for photographing an object under a natural light or a flash exposure mode for photographing an object illuminated by flash light. Said flash exposure mode is further divided into a normal flash exposure mode in which illumination is given to an object in an object field of a low luminance, and a daylight flash exposure mode in which illumination is given to a principal object showing a significant difference in luminance to the background in an object field under natural light illumination. In recent years there has been significant progress in the automation of the camera in order to facilitate photographing without failure in each exposure mode, so that the camera user is being released from the tedious preparations for photographing. Automatic exposure control is already achieved in the natural light exposure mode by an automatic exposure control device capable of controlling the shutter speed and diaphragm aperture for obtaining an appropriate exposure in response to the luminance of the object, and in the normal flash exposure mode by an automatic flash control device capable of controlling the amount of flash given to the object in such a manner as to obtain an appropriate exposure. Also for the daylight flash exposure mode there have been proposed various methods, as disclosed for example in the U.S. Pat. No. 3,792,484, of combining the automatic flash control device with the automatic exposure control device to obtain appropriate exposure for the principal object and the background in the object field. However such known methods are all based on the determination of necessity or intensity of flash illumination according to the luminance or luminance distribution of the object field and the control of a flash unit in response to said determination, and are designed to unconditionally select the natural light exposure mode or the flash exposure mode according to the state of luminance in the object field. It has however been unable, with such prior technologies, to constantly realize ideal exposures intended by the photographer in the various object fields actually encountered. For example in case of photographing a principal object representing a very small area in the entire object field, the flash exposure mode is not selected when the remaining background is of a high luminance, even if the principal object is of a low luminance requiring an artificial illumination. Also in the aforementioned daylight flash exposure mode, the exposure control has to be conducted in such a manner as to obtain an appropriate exposure for the principal object when it is illuminated by flash and simultaneously for the remaining background under the natural light illumination. In order to control the exposure in response to the luminance under natural light illumination in such daylight flash exposure mode, it is already known that a light measurement with plural photosensors corresponding to plurally divided areas in the object field generally provides a better result than a light measurement with a single photosensor.
However, in case a divided area contains a part of an extremely high luminance, for example a direct light from a light source, a part of low luminance also present in said divided area is masked by said high-luminance part, thus merely reducing the difference in luminance among said divided areas and failing to transmit the information on such low-luminance parts, particularly if the number of such divided areas is limited. Consequently an exposure control based on such light measurement will provide a deficient exposure for such low-luminance parts although an appropriate exposure is obtained for the high-luminance parts.